1. Field of the Invention
The present invention relates to a recording unit and an image recording apparatus.
2. Related Background Art
The ink jet recording method is a low-noise and non-impact recording method to record an image by discharging an ink directly on a recording medium. Further, this method does not require a complicated apparatus in operation and hence, a low running cost, miniaturization of the apparatus, and color printing are easy to realize
Therefore, recording apparatuses such as a printer, a copier, a facsimile, a word processor, and the like, to which the ink jet recording method is applied, have been so far put into practical use. By applying such ink jet recording technology, color ink jet recording apparatuses to form a multicolor image using a black ink and a color ink (for example, at least one color ink chosen from a yellow ink, a cyan ink, a magenta ink, a red ink, a green ink, and a blue ink) have also been put into practical use.
On the other hand, the ink jet recording method has a problem that when different two kinds of inks are applied to the recording medium, the inks are mixed with each other on a boundary part between them to cause a phenomenon (bleeding) of lowering a quality of a color image. Particularly, color mixing on the boundary part between the black ink and the color ink considerably influences lowering of the quality of the color image and thus, various methods for solving this problem have been developed.
A representative method for solution is to employ an ink set and a recording method which have, when two kinds of inks are adjacently applied to the recording medium, mechanisms to cause thickening of at least either one or agglomeration and precipitation of at least either one coloring material to prevent bleeding.
For instance, U.S. Pat. No. 5,428,383 discloses that one ink contains a precipitant (for example, a polyvalent metal salt) and a colorant in a form of an organic dye having a carboxyl and/or carboxylate group is adopted for the other ink, preferably the black ink. It is described that when printing is carried out using these inks in adjacent positions each other, a first ink containing the precipitant precipitates the colorant having a carboxyl and/or carboxylate group to prevent movement of the colorant to the other ink, resulting in reduction of bleeding in adjacent two printing areas.
In addition, U.S. Pat. No. 5,976,230 discloses a technology in which applying two kinds of inks reactive to each other to the same area prevents bleeding.
Difference in concentration
By the inventors"" study, it has been confirmed that, as described in the U.S. Pat. No. 5,976,230 described above, in an image yielded by applying two kinds of inks reactive to each other to the same area, the density thereof becomes higher than that of an image produced by an single ink. Also, Japanese Patent Application Laid-Open No 6-171208 filed by the applicant of the present application discloses that shooting a pigment-based black ink and a color ink containing a salt on the same position of a recording medium by the ink jet method yields an image with a density higher than that of a black image formed by using a black ink alone. No problem occurs by an increase in the image density by overlaying of reactive ink sets.
However, when a part formed with a black ink and a part formed by a blend of a color ink and the black ink coexist in a black area in the same document, the image density of black may differ from each other to result in a visually abnormal image. More specifically, when in one document, a black character part (a first character part) having no color background and a black character part (a second character part) having a color background exist and the first character part is formed by a black ink alone and the second character part is formed, in viewpoint of bleeding prevention and according to the method disclosed in U.S. Pat. No. 5,976,230 described above, by overlaying of the black ink and a color ink having the reactivity with the black ink, the density of the first character part and the density of the second character part visually differ from each other distinctly to cause abnormal feeling in some occasions.
As one of the methods for solving this problem a treatment method in which, all black image areas, namely, the first character part in the example described above, is shot with a color ink having mutual reactivity with a black ink to fix the black ink. In this case, a consumption of the color ink increases and the color ink shot in advance has normally high penetrability and therefore, the color ink more easily spreads than the black ink on a recording medium, occasionally resulting in that, for example, in the black character part, the character is visually recognized as outlined by the color ink.
As a result of study in light of the findings described above, the inventors found a technique capable of improving the density of an image formed with a black ink alone almost equal to the density of the image yielded by blending a color ink reactive to the black ink with the black ink and also the technique, which is necessary for the ink jet recording, keeping a color balance after long time conservation of a color-recorded image formed, capable of effective prevention of occurrence of bleeding, and capable of maintaining these functions with good durability.
In addition, a configuration of an ink jet head to be more suitably used when an ink set comprising such a combination of a black ink and a color ink was used, was examined. As a result, the present inventors have concluded that, when using a polyvalent metal salt as a component to impart reactivity between two different kinds of inks, in order to increase durability of a part contacting with the ink, particularly a part on a heat-generating member, in a liquid flow path of the ink jet head, the configuration of the part contacting with the ink containing the polyvalent metal salt is important. And, as such a configuration, formation of an anti-cavitation film having a face contacting with the ink in a form of two layers, of which an upper layer contacting with the ink is made of Ta or TaAl and a lower layer is made of an amorphous alloy containing Ta, was found to be effective for further improving discharge durability for the ink containing the polyvalent metal.
The present invention was created on the basis of the findings by the present inventors.
An object of the present invention is to provide a recording unit and an image recording apparatus, which have a configuration capable of improving discharge durability even when an ink containing a polyvalent metal salt is used, while keeping an advantage of using a polyvalent metal salt.
Another object of the present invention is to provide the recording unit and the image recording apparatus capable of improving discharge durability while keeping the above-described feature of using a black ink and a color ink containing a polyvalent metal salt reactive to the black ink.
A further object of the present invention is to provide a recording unit and an image recording apparatus capable of keeping a color balance after long conservation term of a recorded image formed, preventing effectively an occurrence of bleeding, and keeping durably these functions by using an ink set with almost equal fading property xcex94E of each color ink in case of conserving for a long term.
A still further object of the present invention is to provide a recording unit and an image recording apparatus capable of showing effectively an effect of eliminating a difference in density of an image between a part recorded by a blend of the black ink and the color ink reactive to the black ink as described above and a part recorded by using the black ink alone also in high speed printing by improving shooting precision in high speed printing.
The objects described above can be achieved by the present invention described below. A recording unit according to the present invention comprises an ink housing part for housing an ink containing a coloring material and an aqueous medium, and an ink jet head part for discharging an ink droplet of the ink, wherein the ink is a polyvalent metal salt containing ink further containing a polyvalent metal salt; the ink jet head part has a configuration comprised of a substrate having on a base body, a heat-generating resistor member forming a heat-generating part, an electrode wire electrically connected to the heat-generating resistor member, and an cavitation resistant film provided on the heat-generating resistor member and the electrode wire via an insulating protection layer, a liquid flow path communicating with a discharge port for discharging an ink droplet provided corresponding to the heat-generating part; and the cavitation resistant film comprises at least two layers, of which an upper layer contacting with the ink is a Ta film or a TaAl film, and a lower layer is a layer of an amorphous alloy containing Ta.
Further, an image forming apparatus according to the present invention is an image forming apparatus comprising an ink jet head for discharging an ink containing a coloring material and an aqueous medium, wherein the above-described ink is a polyvalent metal containing ink containing a polyvalent metal salt; the ink jet head part has a configuration comprised of a substrate having on a base body, a heat-generating resistor member forming a heat-generating part, an electrode wire electrically connected to the heat-generating resistor member, and a cavitation resistant film provided on the heat-generating resistor member and the electrode wire via an insulating protection layer, a liquid flow path communicating with a discharge port for discharging an ink droplet provided corresponding to the heat-generating part, the cavitation resistant film comprises at least two layers, of which an upper layer contacting with the ink is a Ta film or a TaAl film and a lower layer is a layer of an amorphous alloy containing Ta.
According to the present invention, for example, by adopting combination of a black ink and a color ink containing a polyvalent metal salt reactive to the black ink, it is realized effects that none of bleeding and white haze occurs in a boundary region between the black ink and other color ink and that a black image formed by overlaying the color ink on the black ink for prevention of bleeding can be formed in a very high density almost the same as that of a black image formed by using the black ink alone to yield a high quality image presenting visually evenness. Further, the cavitation resistant film formed by at least two layers, of which an upper layer contacting with the ink is a Ta film or a TaAl film and a lower layer is a layer of an amorphous alloy containing Ta, is used at a part contacting with the ink on at least the heat-generating resistor member in the liquid flow path of the ink jet head, whereby discharge durability can be further improved keeping such effects.
In other words, in case of using the ink containing a polyvalent metal salt, the part contacting with the ink may corrode during use for a long term to disorder discharge stability and cause deterioration of discharge performance in some occasions corresponding to a material quality thereof. In contrast, by using the cavitation resistant film according to the present invention, durability in the part contacting with the ink is kept to make it possible to further continuously maintain the effect yielded by using the ink containing the polyvalent metal salt. The ink jet head is adapted to the configuration in which a movable member displaceable a position thereof in accordance with occurrence of a bubble in the ink is provided in a region corresponding to the heat-generating member in the liquid flow path, precise shooting of the ink droplet is achieved even in high speed printing, a mixed color itself in the boundary region between the black ink and the color ink is reduced to reduce the occurrence of bleeding and also the difference between density of the image by single use of the black ink using the polyvalent metal salt and the density of the image by blend of the black ink and the color ink is eliminated and thus, the occurrence of bleeding is further effectively reduced.
The reason why the above described effect is obtained in case of applying the combination of the black ink containing the salt and the color ink containing the polyvalent metal salt is that the black ink applied to the recording medium causes rapidly solid-liquid separation in the ink by the salt to left a pigment as a satisfactory solid matter on a surface of the recording medium and as the result, the density increase prominently than an optical density of the image formed by the conventional black ink, in which no salt is contained and the pigment penetrates in an inside of the recording medium, in a high degree not reproducible by adjustment of the density of the coloring material. In addition, the optical density of the image formed by the black ink containing the salt alone presents the high optical density as visually almost equal to the optical density of the image in case where the black ink agglomerates on the recording medium.
In addition, also in case of applying the black ink and the color ink by overlaying to express a monotonous gradation, the following problem takes place: the conventional art causes the difference in optical density by the same reason described above and therefore, in order to make a smooth tone expression, a composition ratio of the black ink and the color ink is limited to cause decrease in a degree of freedom and deterioration of the smooth tone expression itself. However, applying the present invention allows making almost the same as the optical density of the part in which the black ink agglomerates and the optical density of the part formed by only the black ink and therefore, by adjusting a proportion of the color ink added to the black ink, a desired tone expression can be realized and also other effect that the image of a more excellent multigradation expression can be realized is yielded.